The game uses massive amounts of CPU - there's little difference between when it's doing something and idling.
Playing on Linux x64, the CPU usage is at least 100% and temperature goes up to 80° on a Lenovo x230 (sorry, I can't measure exactly because the game is broken now).
I tested the usage and temperatures: the game's processes (nw and exe) use 103% CPU total (Xorg takes another 8%). This total does not change regardless of what happens on the screen. The temperature raises by over 20° compared to desktop, ending up at ~73°.
Since this is a computer with rather good cooling, I can believe that some people find theirs to overheat.
Post edited February 11, 2016 by rhn